1. Field of the Invention
The present invention relates to a measurement apparatus for measuring a light intensity distribution in a plane to be measured, an exposure apparatus that includes the measurement apparatus, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
Hitherto, an exposure apparatus used for manufacturing semiconductor devices exposes a resist applied on a wafer to light to evaluate an image-forming performance of the entire exposure apparatus including a light source, an illumination optical system, and a projection optical system. When the image-forming performance of the exposure apparatus is to be measured by exposing the resist to light, processes including development of the resist and observation of a resist image have to be repeated. Hence, performing measurement procedures can be seriously troublesome work, and it is difficult to measure the performance in a short time.
Regarding such problems, a technique of measuring a light intensity distribution on a wafer surface and evaluating an image-forming performance of an exposure apparatus without exposing a resist to light is suggested in William N. Partlo, Charles H. Fields and William G. Oldham, “Direct aerial image measurement as a method of testing high numerical aperture microlithographic lenses”, J. Vac. Sci. Technol. B, vol. 11 (1993) pp. 2686-2691, and U.S. Pat. No. 5,631,731. These documents disclose a technique of measuring a light intensity on a wafer surface while moving a photodetector, and a mask including a micro-slit and a light-shielding portion, the micro-slit having a width equal to or smaller than a value obtained by dividing a wavelength of exposure light by a numerical aperture of a projection optical system.
In the related art technique for measuring the light intensity on the wafer surface using the photodetector and an opening such as the micro-slit, it is necessary to increase a thickness of the light-shielding portion so as to prevent light (transmitted through the light-shielding portion not occupied by the opening) from being incident on the photodetector. However, an increase in the thickness of the light-shielding portion may cause a non-linear optical effect to appear at the opening. With the effect, a light intensity distribution obtained from light transmitted through the opening may differ from a light intensity distribution obtained from light entering the opening. If the thickness of the light-shielding portion is decreased, the light-shielding portion provides insufficient light-shielding. The influence of light transmitted through the light-shielding portion may be increased.
As described above, the related art technique has a difficulty in accurately measuring an actual light intensity distribution on the wafer surface.